Method of repairing Master Boot Record (MBR) in Windows® XP®

How do you repair Master Boot Record (MBR) in Windows XP?

At the end of the ROM BIOS bootstrap routine (which occurs when your PC first boots up), BIOS reads and executes the first physical sector of the first boot device like the hard disk, CD-ROM or DVD-ROM on the system. This first sector is called the Master Boot Record (MBR), which is also known as the partition table or master boot block. At the start of this sector is a small program which uses the partition information (or partition table) stored at the end of the sector to find out which partition is bootable and then attempts to boot from it. The values in the partition table in MBR depend on the size of the disk and on the logical partitioning on that disk. The DOS Boot Record (DBR) will have the Boot Parameter Block (BPB), which includes logical mapping information for that particular partition. The values in BPB are completely dependent on the size of the partition and the type of file system. These two sectors include the information required to find and recognize the file system used to access the data on the drive. If either of these are corrupt, the data becomes inaccessible, even if there is no damage to the data or the file system itself.

Issues related to MBR and tips to fix them are below:

  • Common issues related to MBR

  • Causes of the issue

  • Tips to solve the problems

Common issues related to MBR

Upon starting your Windows XP based computer you may receive an error message that the operating system is missing or not found. This error typically indicates a corrupt or missing MBR from your PC, or can also be a sign of no active (bootable) partition on the hard disk. Anyhow, BIOS is not capable of transferring control to a valid boot record and displaying this error message before terminating. Upon starting your Windows XP based system you can also receive the error message that the NTLDR is missing. This error points to one of the numerous potential problems, but often indicates a corrupt or missing MBR.

Causes of the issue

There are some kinds of viruses called MBR viruses which are capable of damaging the Master Boot Record of your PC by replacing the original MBR with new one created by them. The original MBR sector will be moved to other spots in the hard drive. These MBR viruses will start when the system boots-up. Other probable reasons are hard drive errors and inappropriate installation of multiple operating systems. The effects of a ruined MBR are due to the complications in starting the computer, inability to boot the computer in Safe Mode and other available options.

Tips to solve the problems

The MS-DOS command Fdisk /mbr will rewrite the MBR on the hard disk, to resolve MBR damage. But remember, that this command is ineffective if your computer is infected with MBR viruses. Another option is to run fixmbr. For this, first restart the computer with a Windows CD where a DVD or CD drive is the primary boot device. Now press the ‘R’ key to start the Recovery Console when prompted. In Recovery Console command prompt, you should type 'fixmbr' and follow the instructions on the screen.

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